This invention relates to appliances such as water heaters and furnaces and, more particularly, to a device for controlling dampers commonly used in such appliances.
In a conventional heating appliance a pipe delivers a fuel such as fuel oil or gas from a fuel source to a burner positioned in a combustion chamber. The pipe routinely includes a valve which controls the flow of fuel to the burner.
Known heating appliances typically include an exhaust vent or flue to direct emissions resulting from combustion away from the combustion chamber of the appliance and into an area, such as the outdoors, where the emissions can dissipate. Exhaust vents, however, also allow heat to escape from the appliance thereby reducing the overall efficiency of the appliance. As a result, conventional gas and oil-fired appliances typically include dampers disposed within an airshaft forming the exhaust vent. The damper opens prior to ignition of the burner in the appliance to allow emissions from combustion to be evacuated from the appliance. After the burner is extinguished and combustion has ended, a signal (such as removal of a voltage) is sent from a thermostat or other agent to a relay control circuit which controls a motor. The motor moves the damper to a closed position, blocking the escape of combustion products through the exhaust vent, thereby trapping the remaining heat. In addition to the damper, conventional oil and gas fired appliances also control one or more valves within a fuel line in order to open and close the valves and the damper in response to predetermined conditions.
Recently gas fired appliances have been developed such as those disclosed in U.S. Pat. No. 6,257,871 B1 and U.S. patent application Ser. No. 09/644,740. Both of these cases are assigned to the assignee of the present invention, and the entire disclosures of both are hereby incorporated by reference. It would be desirable to have a damper control device which could use as many parts in common with the recently developed gas damper control devices yet be operational with other fuels, such as oil. However, gas-fired appliances have operating conditions and design constraints which are different from oil-fired appliances, resulting in somewhat different designs for each. This means that merely switching fuel lines is insufficient to convert from one fuel source to another. For example, in gas fired heating appliances, the heat and products of combustion are of a temperature that allows the damper to be moved to the closed position essentially immediately after the call for heat has been satisfied. However, oil-fired heating appliances operate at higher temperatures than gas-fired appliances. To protect the appliance a time delay device can be used. The time delay device controls the damper so that it stays open for a period of time after a call for heat has been satisfied and combustion has ended.
Known time delay circuitry has been mounted as an add on, separate and spaced apart from the relay control circuitry. However, the mounting assembly of the recently developed vent dampers for gas fired heating appliances is relatively compact, and the existing design used for oil-fired heating appliances would not fit within such a tight package. Also, known oil-fired heating appliances needed double pole relays to accept a required range of amperages and attendant furnace sizes. Accordingly, it would be desirable to have a damper control device suitable for use on heating appliances which use fuels other than gas while incorporating the established mounting assembly of vent dampers for gas heating appliances and also satisfying electrical requirements, i.e., prevent arcing between components.
In accordance with a first aspect, a damper control device comprises a mounting plate, a motor assembly coupled to the mounting plate and having a shaft extending therefrom, and a single circuit board coupled to the mounting plate, having relay control circuitry which rotates the shaft to an open position in response to a first signal, rotates the shaft to a closed position in response to a second signal, and time delay circuitry which holds the shaft in the open position for a period of time after receipt of the second signal. The shaft may be attached to a damper so that the shaft and damper move together. The relay control circuitry may operate on the same current as the first and second signals. Preferably the relay control circuitry uses a single pole relay.